The present invention relates to a thermoplastic bag having integral handles and also to individual bag packs of such bag structures. The type of bag contemplated herein is particularly adapted for use as a grocery sack capable of carrying loads up to about 30-35 pounds.
The present invention also relates to methods and systems for preparing a thermoplastic sack, and, more particularly, to methods and systems for preparing such a sack having at least a substantially flat rectangular bottom. One type of bag contemplated for preparation by a system and process of the present invention is more particularly defined in U.S. Pat. No. 4,554,192, issued Nov. 19, 1985.
For years in the United States the means for carrying items purchased in a grocery store or supermarket has been the paper sack. This sack, as is well known, is made of kraft paper, which has a high beam strength as compared, for example, with thermoplastic film. Thus, bags made of this material, when fully extended, are capable of supporting themselves. When such bags are filled with grocery items, they have the desirable attribute of being able to stand upright. In addition, kraft paper bags are made so as to have opposing gusseted sides and a foldable-extensible rectangular bottom. This type of structure, when fully extended, provides the maximum volumetric efficiency for a container of this type. The volume of such a sack is represented by a rectangular bottom projected to the height of the bag.
These two attributes are about the only positive aspects of kraft paper grocery sacks. When folded and collapsed they are bulky and occupy considerably more space than thin film thermoplastic grocery sacks. Whatever cost advantage paper grocery sacks enjoyed in the past appears to be disappearing. Paper grocery bags are notorious for their lack of wet strength in an environment which constantly exposes them to the deleterious effects of aqueous liquids. This causes the bags to fail and spill their contents on the supermarket floor, the parking lot blacktop, the purchaser's automobile, or during transfer from the automobile to the purchaser's home. The time needed for supermarket employees to fill kraft paper sacks as opposed to thermoplastic film grocery sacks, is on average, longer. Such bags produce paper cuts, which have become an occupational hazard with kraft paper bags. Kraft paper bags have limited re-use possibilities and they are not a stable land fill material.
In the late 1970's and early 1980's, thin film thermoplastic handled grocery sacks began to make significant inroads into an area totally dominated by the kraft paper grocery sack.
U.S. Pat. No. 4,165,832, the disclosure of which is incorporated by reference herein in its entirety, describes to some degree, the evolution of handled bags from the time when handle elements were separately attached to the open mouth portion of the bag. This patent also discusses the improvement of forming an ungusseted bag having integral thermoplastic handles as a part thereof. This ungusseted type of bag is constructed from a pillowcase type blank consisting of two sheets of plastic, e.g., from a collapsed tube, sealed at opposite ends. A U-shaped cutout at one end fashions an opening for the bag and a separate cut or slit opens two loops which constitute the handles of the bag. A further evolution in this bag structure came about when the bag was made to have gusseted sides. This permitted the handles to be fashioned of two layers of film which gave the handles additional strength. In all cases, the bottom of the bag constituted either a heat sealed double layer of film, or in the case of a gusseted structure, the molds of the gusset were sealed at the bottom between the front and back sides of the bag. This latter seal can be considered the "trapped gusset" seal.
Since the late 1970's to the present time, the commercial plastic grocery sack has had a bottom region which has not changed. FIGS. 1-4 of the present application illustrate a thermoplastic film grocery sack of the general type manufactured by almost every thermoplastic grocery sack manufacturer in the United States. This grocery sack is made by collapsing a thermoplastic tube, and while in the process of collapsing, forming therein two side gussets. The gussets are represented in FIG. 2 by in-folded regions 16 and 18 on one side and 20 and 22 on the opposite side. After the gusseted tube has been fully collapsed, it is sealed and severed along lines 26 and 28. Seal line 28 is the handled and open mouth end portion of the bag after plastic film is removed, forming both the bag mouth opening and handles of the bag. Seal line 26 constitutes the closed end of the bag. As will be appreciated, during the sealing of the bottom region of the bag, four films are heat sealed together at the outboard region of the bag, i.e., 12, 16, 18 and 14 on the one side and 12, 20, 22 and 14 on the other side, and in the center region only two films, 12 and 14, are heat sealed together.
This bag bottom structure, adopted almost exclusively by the plastic grocery sack manufacturers, has at least two shortcomings. The first is that whenever there is a thickness transition involving a heat seal, where a thicker region transitions down to a thinner region, as in the gusset region of four layers transitioning at a fold point down to the two layers of the front and rear panels of the sack, a weak spot is created at the fold point. This becomes a tear initiation point as the bag is loaded with goods and the bag tries to expand to accommodate the goods. The bottom of the gusset being trapped and sealed within the front and rear panels of the bag in the regions 32 of FIG. 1 at both bottom outboard regions of the bag cannot expand to accommodate goods in the bottom of the bag as well as it can in the upper midway region of the bag where the side gussets expand to the minimum. FIG. 3 shows a side view of the bag of FIG. 1 in an expanded condition. It will be noted that the lower region 30 of the bag has less effective volume than the central region 34 of the bag. As indicated, because the bottom of the gusset on both sides of the bag is trapped and sealed between the front and rear layers of the bag walls, they cannot expand to accommodate increasing bag expansion caused by goods being loaded therein Weight and hoop stress forces are brought to bear at points 36 on both sides of the bag, with the result that tears in the bottom seal are initiated at these points. This asymmetrical load distribution places no load on the bottom seal between 36 and the bag corner. As the hoop and load forces increase, the tears can progress to permit the product to fall from the bag. Since this type of grocery sack is suspended from its integral handles, there is no bottom support safeguard to protect items from falling through the bottom of such a bag.
The second disadvantageous aspect of such a seal-trapped gusset arrangement, is the fact that the sides of the bag cannot expand to their full width and, thus, full volumetric efficiency is sacrificed. When examined carefully, for example, in a bag as described, measuring 12 inches by 8 inches (4 inch gussets) by 24 inches, including handle length, a significant percentage of the bag film (excluding the handles) does not contribute to bag volume. Over 8% of the bag film is wasted in the bottom of the bag because of the trapped gussets.
U.S. Pat. No. 3,119,548, issued Jan. 28, 1964, describes a thermoplastic bag having a square or rectangular bottom which avoids the trapped gusset structure. This sack, however, is intended as a liner for a cardboard ice-cream container. Thus, this structure never was intended to support product load by means of its own integrity. An outer-container provided shape and support for the thermoplastic liner. This liner is not used with handles.
U.S. Pat. No. 3,580,486 describes a thermoplastic film bag which has a rectangular bottom without a seam or seal, and ungusseted sides which contain three seals when the bag is expanded. This bag contains a center handle which is only one film layer thick because of the ungusseted side structure.
It is an object of the present invention to present a novel thermoplastic film bag and bag pack.
Yet another object of the invention is to present a thermoplastic film handled grocery sack which has maximum volumetric efficiency.
Still another object of the present invention is to present a thermoplastic film grocery sack having seam seals of exceptional integrity.
A further object of the present invention is to present a thermoplastic film handled sack which has a minimum of film not contributing to either volumetric capacity or handle support.
A still further object of the present invention is to present a thermoplastic film grocery sack which contains considerably less raw material for essentially the same volumetric capacity as trapped-gusset bags.
It is an object of the invention to present a process for the preparation of flat bottom sacks.
It is yet another object of the invention to present a process for the preparation of interconnected severable flat-bottomed grocery sacks.
It is still another object of the present invention to present processes of forming flat-bottomed thermoplastic film sacks not having handles.
It is yet another object of the invention to present a process for preparing flat-bottomed handled sacks in bag pack form.
A further object of the present invention is to present novel systems for the preparation of such thermoplastic film flat bottom sacks.